wayland-egl: correct wayland-egl.pc description/version

Drop the "Mesa" part from the commit message and change the version to
17.4.0. The number bears references from its Mesa heritage.

Currently Mesa provides 17.2.x while 17.3.x should be the last version
that ships the library.

Some version numbers of wayland-egl.pc providers and users.
The latter is taken from Ubuntu 17.04.

Providers:
 - Mali: 7.10
 - Mesa: 17.2.2

Users:
 - retroarch: NA
 - qtwayland5: NA
 - mpv, libmpv1: 9.0
 - mesa-utils-extra: NA
 - weston, libweston-1-0: NA

 - libwaffle-1-0: 9.1
 - libsdl2-2.0-0: NA

 - libgstreamer-plugins-bad1.0-0: autotools 9.0, meson 1.0
 - libglfw3-wayland: NA

 - kwin-wayland, kwin-wayland-backend-wayland: NA?
 - glmark2-wayland, glmark2-es2-wayland: NA

 - libwebkit2gtk-4.0-37, libwebkit2gtk-4.0-37-gtk2, (webkit overall): NA
 - libgtk-3-0 (gtk overall): NA
 - libcogl20 (cogl overall): 1.0.0

v2: Bump the version to 17.4.0

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Arnaud Vrac <avrac@freebox.fr>